I want to be clear that I have the greatest respect for Stack Overflow. I think there has been nothing ever that has increased programmer productivity more than Stack Overflow. (quoting wikipedia http://en.wikipedia.org/wiki/No_Silver_Bullet) Fred Brooks said that "there is no single development, in either technology or management technique, which by itself promises even one order of magnitude [tenfold] improvement within a decade in productivity, in reliability, in simplicity." But Stack Overflow hadn't been born at that time. No language, operating system or compiler could ever have more impact on developer productivity than an effective global Q&A site for programmers - that's what Stack Overflow is and it is damn fine.
It's just that Stack Overflow would be diluted and weakened by allowing open ended discussion on software technology and development. People go to SO with questions for which they want a specific answer.
Not Constructive is intended to facilitate the valuable discussions about software that don't fit into that strict Q&A format. Not Constructive is for broader questions, and welcomes subjective opinion. It's not in conflict with SO, it's a complement to SO.
Please do sign up at http://signup.notconstructive.com if you're interested in hearing when we launch.